The effects of hormones on the induction of ornithine decarboxylase (ODC), S-adenosylmethionine decarboxylase (SAMDC), and polyamine levels in vivo are being studied. Previous studies have shown that ODC induction may be a marker for tumor promoters. Hormones often increase the biological activities of complete carcinogens. ODC is used to study the degree of biochemical similarity between hormones and promoters. The present studies indicate that estradiol produces renal adenocarcinomas in the hamsters and induces renal ODC and SAMDC in both the rat and hamster. The induction of renal ODC in the rat by estrogens is proportional to their binding in vitro to cytoplasmic estradiol binding sites. ODC levels in the ovary and uterus of female rats are inversely correlated with each other.